The overall objective of experiments outlined in this proposal is to study mechanisms of viral latency in the Epstein-Barr virus system and to identify events leading to activation of viral replication. The experiments are predicated on biologic differences which have been discovered in the last granting period between standard EB viruses which remain latent and defective or "het" strains which do not remain latent and which activate replication. Many experiments focus on the control of expression of an EBV gene, ZEBRA, which activates replication. We will determine, at first by transcriptional analysis how this control differs in the standard and defective viruses. We will attempt to learn how ZEBRA functions by exploration of its viral targets, purification of the ZEBRA polypeptide and studying ZEBRA-DNA and ZEBRA-protein interactions. By analysis of defective variants we hope to learn which viral sequences are responsible for failure of defective viruses to remain latent. We will also attempt to locate replicative origins of DNA synthesis on defective and standard EBVs. The proposed experiments combine biologic, molecular, genetic and biochemical techniques to explore questions bearing on the switch between latency and replication.